The invention relates to a mixture-compressing internal-combustion engine with secondary-air injection and with air-mass metering in the suction pipe.
Internal-combustion engines of this type, such as are already known in the applicant's "Mercedes" series vehicles, are equipped with secondary-air lines, by which air sucked in by a secondary-air pump and filtered when the internal-combustion engine is in the running-up phase in conveyed to the exhaust-gas side via a controlled secondary-air cut-off valve. This ensures an accelerated response behavior of the catalysts.
Furthermore, the internal-combustion engine has a sequential fuel injection which supplies each cylinder with the correct quantity of fuel at the optimum time.
An object on which the invention is based is, in an internal-combustion engine of the relevant generic type, to provide measures by which further improvements as regards the mixture preparation and the reduction of harmful exhaust-gas constituents can be obtained in the starting and the running-up phase.
According to the invention, this object is achieved by an arrangement comprising:
a suction pipe provided with a throttle flap and an air-mass meter and opening to an engine cylinder inlet valve,
a secondary-air line leading to a exhaust line in bypassing relationship to the suction pipe,
a secondary-air cut-off valve in the secondary-air line,
secondary-air cut-off valve control apparatus for opening the secondary-air cut-off valve during an engine running-up phase,
an injection valve for sequential fuel injection into the suction pipe,
an additional air line leading to the injection valve for selectively providing air assistance to fuel injection,
an air shut-off valve in the additional air line,
and air shut-off valve control apparatus for opening the air shut-off engine valve at least during engine starting and an engine running up phase.
By the use of an air-assisted injection valve with a controlled air supply, the air being taken from the existing secondary-air injection both in the starting phase and in the running-up phase, the air mass hitherto insufficient in these phases can be matched to the air requirement of the air-assisted injection valve necessary for an optimum mixture preparation.
Although an internal-combustion engine with an air-assisted injection valve is known from U.S. Pat. No. 4,557,241, nevertheless in this arrangement the air assistance takes place in a relatively uncontrolled manner.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.